It is often necessary to make checks in an industrial plant in order to determine the evolution undergone by materials of which certain parts of the plant are made, or in order to check that no sensitive parts show signs of dangerous deterioration. It may be necessary to make these checks at a distance because the parts requiring checking are not accessible or because the conditions prevailing in the industrial plant are dangerous to an operator.
For example, when the tubes of steam generators in pressurized water nuclear reactors are checked, it is necessary to operate at a distance from outside the steam generator and beneath its water tank. Checking steam generator tubes in a pressurized water nuclear reactor generally consists in introducing ultrasonic or eddy current probes into the tubes, these probes transmitting the results of their measurements through cables of great length, of which the end not connected to the probe is in electric contact with an apparatus processing the measurement signals.
These cables generally consist of a number of conductors transmitting different measurement signals to the apparatus processing these signals.
The movement of the probes inside the plant being checked, for example inside the tubes of a steam generator, is very often effected by a pushing or pulling action applied to a part of the cable situated outside the installation. This pushing or pulling action may be applied by hand with the aid of an electromechanical control unit called a puller-pusher. The cable has sufficient rigidity to allow pulling or pushing forces to be transmitted to its end carrying the probe.
The opposite end portion of the cable to that carrying the probe is generally wound on a reel of cylindrical shape, which makes it possible to reduce the risk of mechanical damage to the cable and kinking, which could result in a blockage.
The end of the cable which has to make electric contact with the measurement signal processor shares in the rotation of the reel, so that it is necessary to use multitrack rotating connections, each of the conductive tracks corresponding to one measuring conductor. The construction of these connectors gives rise to technical problems which are difficult to solve, and makes it necessary to select suitable materials for ensuring good transmission of the signals. The cost of these connectors is therefore high. In addition, the use of these connectors makes it necessary to take special precautions, which are not always sufficient to avoid all risk of parasites. These parasites, superimposed on the measurement signals and due in particular to bad contact between the brushes and the tracks of the connectors, may give rise to measurement errors resulting in unsatisfactory checks.
Cable winding and unwinding devices have been proposed, in which one end of the cable remains fixed, so that the use of a rotating connector is not required. Devices of this kind cannot, however, be applied to a cable moved by pushing and pulling.
Devices are also known for winding wires, particularly wire rods, which comprise a cylindrical wire receiver casing and a guide duct through which the wire passes. This guide duct carries the wire to the peripheral part of the casing in which the wire is wound. The cylindrical casing is rotated about its axis, so that the relative rotational movement between the casing and the guide duct carrying the wire enables the wire to be wound inside the casing. Nevertheless, a device of this kind has never been used in the case of a measurement cable moved by pushing and pulling, and in addition it would not make it possible to receive the measurement signals in a simple manner.